Display means of this type which have been in existence to date have the deficiency that the quality of the transmission of information is very dependent on the relative position of the observer and the display means. In the case of public clocks it has been attempted to overcome this disadvantage by providing several clock faces around the tower supporting the clock. However, this involves a corresponding additional expenditure and, in any case, where four clock faces are provided on the sides of a square tower, an observer standing at an angle of 45 degrees to two clock faces can still only read the time with difficulty.
For clocks, as well as for advertising displays, it has therefore already been proposed to fasten the entire display vertically on a vertical rotary shaft, and to rotate the shaft slowly by means of a motor. Because of the slowness of the movement it can take some time until the display is aimed at an observer, so that the purpose of the means, especially in the case of an advertising surface, is often lost.
At sports events, display means are occasionally used which represent a compromise between the two aforementioned solutions: here, several display means facing in various directions are mounted, each of which also describes a pivoting movement. This solution is naturally relatively expensive.
UK Patent Specification No. 2 054 901 discloses display means comprising a cylindrical display surface for directing images of an object in all directions and optical bundling aperture means in a form of elongate lenses arranged side-by-side, so as to form a hollow cylinder. However, in this case, the display surface consists of a series of specially photographed views of an object which cooperates with the lenses to provide a three-dimensional view of the object. The display surface does not move so as to direct an image along an angularly movable axis as required by the present invention and the aperture means are designed to expose the same adjacent portions of the display surface along widely divergent axis.
U.S. Pat. No. 4,158,487 discloses similar display means comprising a cylindrical display surface, a rotatable light source directed radially through the display surface, and a concave mirror for reflecting light from adjacent portions of the display surface. Although the rotatable light source directs different parts of the image along an angularly movable axis, the image does not move and the light reflected from the concave mirror is not prevented from being transmitted at an angle to the movable axis.
U.S. Pat. No. 3,463,581 discloses display means in which a cylindrical display surface can be moved so as to direct an image displayed on the display surface along an angularly movable axis and in which aperture means are provided for simultaneously exposing adjacent portions of the display surface along lines of sight which, for each position of the movable axis, correspond with respective adjacent portions. However, these aperture means do not prevent light from being transmitted from said adjacent portions of the display surface along widely divergent axis.
U.S. Pat. No. 3,324,760 discloses display means in which a display surface, in the form of a rotatable mirror, projects an image along an angularly movable axis and aperture means rotatable with the display surface are provided for exposing adjacent portions of the display surface along lines of sight which, for each position of the movable axis, correspond with respective adjacent portions. However, the apparatus is designed to display three-dimensional images in which the lines of sight from the two eyes of an observer emanate from different portions of the display surface. To obtain this effect, it is necessary to ensure that the aperture means consist of only one viewing slot and this reduces the light reflected from the display surface.
Known forms of display means which to some extent overcome these difficulties and deficiencies comprise a display surface for displaying an illuminated image which is to be directed along an angularly movable axis; image movement means for moving the display surface so as to swing the angularly movable axis about a rotational axis; and aperture means for exposing adjacent portions of the display surface along lines of sight which, for each position of the movable axis, correspond with respective adjacent portions.
In one such known form of display means disclosed in German Published Patent Specification No. 1 123 626, the display surface extends across the diametral plane of a cylindrical drum and is rotated at high speed with the drum. The aperture means comprise an elongate slot in the drum which extends parallel to the rotational axis of the drum so that, during a portion of each revolution of the drum, regardless of the directions in which an observer views the display means, the slot scans the width of the display surface at least 48 times a second. As a result of the persistence of vision, the display surface appears to be stationary.
UK Patent Specification No. 299 788 discloses a similar apparatus in which the display surface is not mounted on a diametral plane within the drum and, instead, is mounted so as to provide an arcuate surface surrounding the slot in the drum. This provides a less distorted view of the display surface. However, in both cases, effectiveness of this apparatus is limited because the display surface is viewed through a single slot and this limits the amount of light transmitted from the apparatus and thus the visability of the display surface.